System and method for cell-specific control of three-terminal cells

ABSTRACT

A system and method are described permitting a sophisticated control of a battery composed of a multiplicity of three-terminal electrochemical cells. Each cell has first and second terminals, connected with respective electrodes, one of which is a positive terminal and one of which is a negative terminal. Each cell has a third terminal connected with a grid electrode. A battery is composed of N cells. For each of the N cells, there is provided a respective capacitor switchably coupled to the second and third terminals thereof. A controller is connected through a switching matrix to the capacitors. In operation, the controller is connected sequentially to each capacitor among the multiplicity of capacitors, during which time the capacitor is momentarily uncoupled from its respective cell. When the controller is connected to one of the capacitors, it measures the voltage thereupon. The controller can then charge up or discharge the capacitor to drive it to a desired voltage level. Thereafter, the capacitor is disconnected from the controller and is coupled again to its respective cell.

When large amounts of energy are to be stored to and retrieved from abattery composed of three-terminal electrochemical cells, many competinggoals need to be satisfied, including but not limited to the following.It is desired to provide a long service life for the battery. It isdesired to maximize the energy density of the storage. It is desired tominimize the risk of failure of any particular cell in the battery. Itis not easy to satisfy all of these goals simultaneously, and it is noteasy to satisfy all of these goals at an acceptable cost. As will bedescribed below, the invention relates generally to control of a batterycomposed of a multiplicity of three-terminal electrochemical cells, andcan also relate to a single three-terminal electrochemical cell.

BACKGROUND

The classical voltaic cell stores electrical energy between twoelectrodes, and the energy is stored by electrochemical means. Such acell is sometimes called a “Faradaic” cell to distinguish it from aclassical capacitor which stores electrical energy in an electrostaticfashion. The classical cell is a two-terminal device. In most industrialand automotive applications, a multiplicity of voltaic cells are placedin series, defining a battery. In some applications, the cells areplaced in series-parallel combinations, defining a battery. The batteryis charged and discharged hundreds or thousands of times during itsservice life. Each cell has two electrodes, typically composed ofnon-identical metals or other conductive materials, with an electrolytedisposed between the electrodes.

From time to time it has been proposed to place a third electrode in avoltaic cell. It has been proposed that the third electrode might beused for sensing voltage, so as to arrive at an estimate of someparameter of interest in the cell. See for example P. F. Grieger et al.,“Sealed battery with charge-control electrode”, U.S. Pat. No. 3,424,617A, Jan. 28, 1969, and H. Reber, “Hermetically sealed storage batteryincluding an auxiliary electrode”, U.S. Pat. No. 3,462,303 A, Aug. 19,1969.

SUMMARY OF THE INVENTION

A system and method are described permitting a sophisticated control ofa battery composed of a multiplicity of three-terminal electrochemicalcells. Each cell has first and second terminals, connected withrespective electrodes, one of which is a positive terminal and one ofwhich is a negative terminal. Each cell has a third terminal connectedwith a grid electrode. A battery is composed of N cells. For each of theN cells, there is provided a respective capacitor switchably coupled tothe second and third terminals thereof. A controller is connectedthrough a switching matrix to the capacitors. In operation, thecontroller is connected sequentially to each capacitor among themultiplicity of capacitors, during which time the capacitor ismomentarily uncoupled from its respective cell. When the controller isconnected to one of the capacitors, it measures the voltage thereupon.The controller can then charge up or discharge the capacitor to drive itto a desired voltage level. Thereafter, the capacitor is disconnectedfrom the controller and is coupled again to its respective cell.

DESCRIPTION OF THE DRAWING

The invention will be described with respect to a drawing in severalfigures, of which:

FIG. 1 shows a system for controlling a battery, including modules forindividual control of voltages at grid (third) electrodes of cells, andmonitoring thereof;

FIG. 2 shows a driver and sensing system 121 for use in the system ofFIG. 1;

FIG. 3 shows a load and charging system 105 forming part of the systemof FIG. 1;

FIG. 4 shows an exemplary three-terminal electrochemical cell such asmight be used in the system of FIG. 1;

FIG. 5 shows a detail of a second approach for the modules of FIG. 1;

FIG. 6 shows a controller for controlling the modules of FIG. 5; and

FIG. 7 shows a detail of a third approach for the modules of FIG. 1.

Where possible, like reference numerals have been used in the variousfigures to denote like elements.

DETAILED DESCRIPTION

Turning first to FIG. 4, there is shown a three-terminal electrochemicalcell. Ignoring for the moment the electrode 133 and the terminal 134, wesee a conventional electrochemical cell with positive terminal 131 andnegative terminal 132. An electrolyte, omitted for clarity in FIG. 4 isdisposed between the positive and negative terminals. A third terminal134 sets this cell apart from the majority of electrochemical cellswhich have two terminals. The third terminal 134 connects with a grid133. The grid 133 lies within the electrolyte and may be compared insome ways with a grid of a triode vacuum tube, and may be compared insome ways with the gate of a field-effect transistor (“FET”). Asmentioned above, it has been reported that some investigators haveinserted such a grid into an electrochemical cell so as to facilitatethe monitoring of electrical potential (voltage) at some point betweenthe positive and negative terminals. In the system according to theinvention, it is contemplated that the third terminal 134 and grid 133are used not only for sensing purposes but also for control purposes,with some electrical potential applied to the grid so as to influencethe function of the cell, for example during charging time or duringdischarging time.

The specific use to which the grid and third electrode will be put in aparticular cell are a function of the particular chemistry selected forthe cell (for example the composition of the positive and negativeelectrodes and the selection of electrolyte) and the physical structure(for example electrode surface structure). In one type of cell, the gridvoltage might be employed to control (and perhaps to slow down) acharging current to permit an electrode surface to more readily absorbions in a controlled way. This might be done to attempt to maximize theservice life of the cell, or might be done to attempt to maximize theenergy storage capacity of the cell.

In general, such an electrochemical cell is not employed in isolationbut forms part of a battery (a number of cells in series). In such abattery the grids might be employed to maximize the performance ofbattery (for example, attempting to maximize service life or energystorage capacity), in which case the grids of the various cells might bedriven in more or less the same way. But in such a battery, anotherpossibility is that the grids might be employed as well as part of acell balancing system. If a particular cell were seen to be out ofbalance with its neighbors, the grid of that cell might be driven in aparticular way, driven rather differently than the grid drive for theneighboring cells.

It will be appreciated that the cell balancing approach described herehas an advantage over a traditional cell balancing approach in whichresistors are used to draw down particular cells so as to bring aboutbalancing. The resistor approach wastes energy due to heat dissipationin the resistors.

It will be appreciated that in many implementations, the grid 133 isinsulated chemically and electrically from the electrolyte of the celland from the positive and negative electrodes of the cell. If it isinsulated, then very little current would ever flow into or out of thecell via terminal 134. The current flow would be the modest amount ofcurrent flow needed to bring about some desired potential at the grid.

Another possibility is that the grid 133 is selected to be some materialthat is nonreactive in the relevant context. Thus for some cellchemistries, the grid might be made of platinum and might not need to beinsulated because platinum is nonreactive in the relevant context.

It is also possible the grid 133 might be neither insulated from theelectrolyte nor nonreactive relative to the electrolyte.

We turn now to FIG. 1. FIG. 1 shows a battery 101 composed of individualcells such as cell 104 of FIG. 4. The battery 101 is connected via lines127, 128 with circuitry 105 which in a general way might include a load(such as motors in an electric car) and might include a charging systemfor recharging the battery 101.

We now turn to FIG. 3. FIG. 3 shows a typical circuitry 105 as inFIG. 1. Circuitry 105 includes a load 130 (for example a motor in anelectric car) and a charging system 129 for recharging the battery.

Returning to FIG. 1, we see that each cell 104, 103, 102 in the battery101 is in series with the other cells of the battery. Each cell has a“third electrode” as discussed in connection with FIG. 4. Each cell hasa respective module 204, 203, 202 connected with the grid and anotherterminal thereof. The modules 204, 203, 202 are collectively termed abattery control apparatus 207. Each of the modules such as module 204 iscontrolled so as to apply some desired electrical potential (voltage) tothe grid and other terminal of the respective cell such as cell 104.

Each module 204, 203, 202 may be an electronic driver, which produces avoltage according to a digital word stored in it, and which is convertedto analog form through a D/A converter. As will be discussed below,other approaches may also be employed for the modules 204, 203, 202.

Turning momentarily to FIG. 6, there is shown a controller 209 whichcontrols the modules 204, 203, 202. The controller 209 may receiveinformation about current flowing into the load 130 or information aboutcharging current sourced from the charging system 129. The controller209 controls the various modules 204, 203, 202 so as to bring aboutdesired potentials at the respective grids of the respective cells. Thecontroller 209 may also collect information from the various modules204, 203, 202 so as to ascertain the actual potential at the respectivegrids. In this way the controller 209 may gain information for exampleabout the state of charge of each cell or information about the chemicalcondition of each cell.

As was mentioned above, each module 204, 203, 202 may be an electronicdriver. Turning now to FIG. 5, what is shown is a detail for a secondapproach for the modules of FIG. 1. Each module 204, 203, 202 has arespective capacitor 112, 113, 114 connected between the grid terminalof its respective cell and between one of the other cell terminals. InFIG. 5 it is portrayed that the capacitor is connected with the grid andwith the negative terminal of the cell. It will be appreciated that thecapacitor could, without departing from the invention, likewise insteadbe connected with the grid and with the positive terminal of the cell.

The connection of a capacitor (for example 112) to its respective cell(for example 104) is by means of switches (for example 106, 107). Theswitches might be traditional electromechanical switches (relays). Butmore likely the switches will be solid-state switches. Such switches areseen at 106, 107, 108, 109, 110 and 111.

Also provided are switches (for example 115, 116, 117, 118, 119 and 120)that selectively couple one or another of the capacitors 112, 113, 114with a driver 121 with leads 122, 123 (shown in FIG. 2).

During the time that a particular capacitor (for example 114) isdisconnected from its grid, it may be desired to maintain a particularpotential at that grid. If so, then as shown in FIG. 5, optionally someadditional capacitors 314, 313, 312 may be provided. As for capacitor114, when it is disconnected from its grid, capacitor 314 may beswitched into place to maintain a particular potential at that grid.Just as each capacitor 114 has four switches 106, 107, 115, 116 aroundit, so that the capacitor 114 may be selectively connected with the gridor with the driver 121, so likewise each capacitor 314 has four switchesaround it, accomplishing similar selective connection with the grid orwith the driver 121. The four switches around capacitor 314 areunlabeled for clarity but their function is apparent to the alert readerfrom the present discussion.

It will be appreciated that in the arrangement of FIG. 5, the number ofswitches may be around four times the number of cells if no additionalcapacitors 314, 313, 312 are provided. If the additional capacitors 314,313, 312 are provided, then the number of switches may be around eighttimes the number of cells. But returning to FIG. 1, more generally theindividual voltage control on the grids of the cells might use differentcircuitry than what is shown in FIG. 5. So returning briefly to FIG. 1,the number of switches might be some number other than four times thenumber of cells. Or the modules 204, 203, 202 might use completelydifferent ways to isolate the grids from each other.

More will be said about the driver 121 in connection with FIG. 2. Thedriver 121 may have a microcontroller 126 with a control line 135 to thecontroller 209. The controller 209 may be provided information about thesystem, such as the temperature of the battery 101, the measureddischarge current when the battery 101 powers the load 130, or themeasured charging current when the charging system 129 tries to chargeup the battery 101. The measurements of current are carried out by meansof a current measurement process, the details of which are omitted forclarity in FIG. 1. The measurement of battery temperature is likewisecarried out by a temperature sensor at the battery, omitted for clarityin FIG. 1.

Also visible in FIG. 2 is a voltage driver 124 which is intended to beable to force the potential in one of the capacitors 112, 113, 114 tosome desired potential. Also visible in FIG. 2 is a sensing amplifier125. This amplifier 125 provides information of interest to themicrocontroller 126, namely the sensed potential on one or another ofthe capacitors 112, 113, 114.

An exemplary voltage driver 124 may be relatively low impedance when itis trying to drive a capacitor to some desired potential and may berelatively high impedance if it is not trying to drive the capacitor atall. An exemplary amplifier 125 will have a very high input impedance atlines 122, 123 so that it does not disturb the conditions being measuredsuch as the potential on the capacitor such as 112, 113, 114.

Switches 316, 318 may be employed to permit the voltage driver 124 to beselectively connected or not connected with the lines 122, 123. Switches317, 319 may be employed to permit the amplifier 125 to be selectivelyconnected or not connected with the lines 122, 123.

It will be appreciated that what is shown in FIG. 5 is a switchingmatrix with four times as many switches as there are cells to control.The switching matrix is controlled with control lines controlled bycontroller 209. The control lines are omitted for charity in FIGS. 1 and2.

A typical sequence of steps in connection with FIG. 5 is as follows.First, as a general rule, most of the time each capacitor 112, 113, 114is connected with its respective cell 104, 103, 102. As mentioned above,each grid 133 may be insulated, in which case the charge on thecapacitor may stay substantially unchanged for some period of time. Oras mentioned above, the grid 133 may be a material that is electricallyconductive but is not chemically reactive in its context (perhapsplatinum), and again this may lead to the charge on the capacitorstaying substantially unchanged for some period of time.

With the passage of time, the charge on a capacitor might change, forexample due to a substantial running-down of a cell (due to dischargeinto a load) or due to a substantial charging-up of a cell.

A next step is that cell-side switches (for example 106, 107) are openedso that a selected capacitor (for example 112) is no longer connectedwith its respective cell (for example 104). After the cell-side switchesare opened, then controller-side switches (for example 115, 116) areclosed. This connects the selected capacitor with the driver 121.

It is desirable that this switching be break-before-make. This protectsthe driver 121 from having to deal with the (sometimes very high)voltages present at some points in the battery 101. In an electric car,for example, the battery voltage might be 400 volts or 600 volts.Preserving a break-before-make regime in the switching matrix saveshaving to “float” the driver 121 and saves having to rate itsconnections and insulation at such high voltages.

Once the selected capacitor is connected with the driver 121, typicallythe first step will be to measure the voltage on the capacitor by meansof sensing amplifier 125, at a time when the voltage driver 124 has afloating (high impedance) output. If desired, the driver 121 may “touchup” the voltage on the capacitor by means of the voltage driver 124,perhaps drawing down the voltage on the capacitor or charging up thecapacitor. It will be noted that the sensing amplifier 125 permits themicrocontroller 126 to know what has been accomplished by the voltagedriver 124. For example the voltage driver 124 may be “turned on” in adirection that tends to charge or discharge the capacitor, and sensingamplifier 125 may be employed to monitor the voltage on the capacitor,so that the microcontroller 126 can “turn off” the voltage driver 124when the desired voltage has been reached.

The controller-side switches would then be opened, and after this, thecell-side switches would be closed, reconnecting the capacitor with itsrespective cell.

Depending upon the detailed goals of the battery control apparatus, itmay be intended that the voltage at a particular grid remain constant ornearly constant even during the time that an associated switchablecapacitor is disconnected from the grid. There are several approachesthat might be followed to make this possible.

One possibility as mentioned above is to double the number of switchablecapacitors so that each cell has two respective switchable capacitors,and at any given instant one capacitor or the other is being employed toforce the grid to a desired voltage.

Regardless of the details of the battery control apparatus design, theprocess discussed in connection with FIG. 5 is then repeated for theother capacitors, until all of the capacitors have been checked to seewhat voltage they contain and each capacitor driven up or down involtage as desired.

The process is then repeated for all of the capacitors from time totime, so as to learn what voltages are present at the various capacitorsand so as to drive the capacitors to desired voltages.

FIG. 7 shows a detail of a third approach for the modules of FIG. 1.Each module 204, 203, 202 has a respective capacitor 112, 113, 114connected between the grid terminal of its respective cell and betweenone of the other cell terminals. In FIG. 7 it is portrayed that thecapacitor is connected with the grid and with the negative terminal ofthe cell. It will be appreciated that the capacitor could, withoutdeparting from the invention, likewise instead be connected with thegrid and with the positive terminal of the cell.

The connection of a capacitor (for example 112) to its respective cell(for example 104) is by means of switches (for example 106, 107). Theswitches might be traditional electromechanical switches (relays). Butmore likely the switches will be solid-state switches. Such switches areseen at 106, 107, 108, 109, 110 and 111.

Also provided are switches (for example 115, 116, 117, 118, 119 and 120)that selectively couple one or another of the capacitors 112, 113, 114with a driver 121 with leads 122, 123 (shown in FIG. 2).

During the time that a particular capacitor (for example 114) isdisconnected from its grid, it may be desired to maintain a particularpotential at that grid. If so, then as shown in FIG. 7, an additionalcapacitors 315 may be provided. As for capacitor 114, when it isdisconnected from its grid, capacitor 315 may be switched into place tomaintain a particular potential at that grid. Just as each capacitor 114has four switches 106, 107, 115, 116 around it, so that the capacitor114 may be selectively connected with the grid or with the driver 121,so likewise capacitor 315 has many switches around it, accomplishingsimilar selective connection with any of the grids of the cells or withthe driver 121. The switches around capacitor 315 are unlabeled forclarity but their function is apparent to the alert reader from thepresent discussion.

It will be appreciated that in the arrangement of FIG. 7, the number ofswitches may be around six times the number of cells.

The switching matrix of FIG. 7 is controlled with control linescontrolled by controller 209. The control lines are omitted for charityin FIG. 7.

A typical sequence of steps in connection with FIG. 7 is as follows.First, as a general rule, most of the time each capacitor 112, 113, 114is connected with its respective cell 104, 103, 102. As mentioned above,each grid 133 may be insulated, in which case the charge on thecapacitor may stay substantially unchanged for some period of time. Oras mentioned above, the grid 133 may be a material that is electricallyconductive but is not chemically reactive in its context (perhapsplatinum), and again this may lead to the charge on the capacitorstaying substantially unchanged for some period of time.

With the passage of time, the charge on a capacitor might change, forexample due to a substantial running-down of a cell (due to dischargeinto a load) or due to a substantial charging-up of a cell.

A next step is that cell-side switches (for example 106, 107) are openedso that a selected capacitor (for example 112) is no longer connectedwith its respective cell (for example 104). After the cell-side switchesare opened, then controller-side switches (for example 115, 116) areclosed. This connects the selected capacitor with the driver 121.

The controller-side switches would then be opened, and after this, thecell-side switches would be closed, reconnecting the capacitor with itsrespective cell.

As shown in FIG. 7, it may be intended that the voltage at a particulargrid remain constant or nearly constant even during the time that anassociated switchable capacitor is disconnected from the grid.

The capacitor 315 is switched into place at a particular grid during thetime that its respective capacitor is uncoupled from the grid.

The process discussed in connection with FIG. 7 is then repeated for theother grids, until all of the capacitor that correspond with a grid havebeen checked to see what voltage they contain and each capacitor drivenup or down in voltage as desired.

The process is then repeated for all of the capacitors from time totime, so as to learn what voltages are present at the various capacitorsand so as to drive the capacitors to desired voltages.

In this way, the system may permit cell balancing. If it is learned thatsome cell is unbalanced relative to its neighbors, the selectivetweaking of charge on the capacitor connected with that cell may tend tobring the cell back into balance.

The sensing by means of the grid electrodes may permit the driver 121and controller 209 to arrive at a prediction of imminent failure of acell, thus permitting the battery to be taken out of servicechronologically prior to such failure.

The system may, in this way, permit more careful control of boundaryconditions such as electrode management at extreme times (electrodenearly saturated with ions during charge, or electrode nearly empty ofions during discharge), thus permitting optimization of battery capacityor battery life.

The system and method are shown in a system in which each capacitor isconnected with the grid electrode and with the negative electrode of therespective cell. But another approach is that each capacitor isconnected with the grid electrode and with the positive electrode of therespective cell. One approach or the other might be optimal dependingupon cell chemistry or physical configuration of the cells.

The alert reader will appreciate that other obvious changes andimprovements can be made to the system and method without departingtherefrom. Any such changes and improvements are intended to beencompassed by the claims which follow.

The invention claimed is:
 1. A battery control apparatus for use with abattery composed of a multiplicity of three-terminal electrochemicalcells, each cell having first and second terminals, connected withrespective electrodes, one of which is a positive terminal and one ofwhich is a negative terminal, and each cell having a third terminalconnected with a grid electrode, the apparatus comprising: for each cellamong the multiplicity of cells, a respective module coupled to thesecond and third terminals thereof; and a controller; the controllerdisposed to control each of the respective modules to bring about arespective desired potential across the respective second and thirdterminals thereof; and further comprising the battery composed of themultiplicity of three-terminal electrochemical cells, wherein each cellcontains an electrolyte and the grid of each cell is insulated from theelectrolyte.
 2. A battery control apparatus for use with a batterycomposed of a multiplicity of three-terminal electrochemical cells, eachcell having first and second terminals, connected with respectiveelectrodes, one of which is a positive terminal and one of which is anegative terminal, and each cell having a third terminal connected witha grid electrode, the apparatus comprising: for each cell among themultiplicity of cells, a respective module coupled to the second andthird terminals thereof; and a controller; the controller disposed tocontrol each of the respective modules to bring about a respectivedesired potential across the respective second and third terminalsthereof, and further comprising the battery composed of the multiplicityof three-terminal electrochemical cells, wherein each cell contains anelectrolyte and the grid of each cell is selected to be some materialthat is nonreactive in the context of the cell.
 3. A method for use witha battery control apparatus for use with a battery composed of amultiplicity of three-terminal electrochemical cells, each cell havingfirst and second terminals, connected with respective electrodes, one ofwhich is a positive terminal and one of which is a negative terminal,and each cell having a third terminal connected with a grid electrode,the battery control apparatus comprising a multiplicity of modules eachcorresponding to one of the three-terminal electrochemical cells, eachmodule connected with the second and third terminals thereof, the methodcomprising: from time to time, controlling each of the modules so as todrive the voltage across the second and third terminals to a respectivevoltage level; wherein each of the modules comprises a respective firstcapacitor and switchable coupling to the second and third terminals ofthe respective cell, the method further comprising coupling the firstcapacitor to its respective cell; from time to time, uncoupling one ofthe first capacitors from its respective cell and coupling the capacitorwith a controller comprising a driver, and driving the voltage thereofto a voltage level; wherein each of the modules comprises a respectivesecond capacitor and switchable coupling to the second and thirdterminals of the respective cell, the method further comprising couplingthe second capacitor to its respective cell; from time to time,uncoupling one of the second capacitors from its respective cell andcoupling said one of the second capacitors with the controllercomprising the driver, and driving the voltage thereof to a voltagelevel; and wherein the coupling of the first and second capacitors iscarried out so that when the first capacitor is uncoupled from its grid,the second capacitor is coupled thereto, and vice versa.
 4. A method foruse with a battery control apparatus for use with a battery composed ofa multiplicity of three-terminal electrochemical cells, each cell havingfirst and second terminals, connected with respective electrodes, one ofwhich is a positive terminal and one of which is a negative terminal,and each cell having a third terminal connected with a grid electrode,the battery control apparatus comprising a multiplicity of modules eachcorresponding to one of the three-terminal electrochemical cells, eachmodule connected with the second and third terminals thereof, the methodcomprising: from time to time, controlling each of the modules so as todrive the voltage across the second and third terminals to a respectivevoltage level wherein each of the modules comprises a respective firstcapacitor and switchable coupling to the second and third terminals ofthe respective cell, the method further comprising coupling the firstcapacitor to its respective cell; from time to time, uncoupling one ofthe first capacitors from its respective cell and coupling the capacitorwith a controller comprising a driver, and driving the voltage thereofto a voltage level; wherein the apparatus comprises an additionalcapacitor and switchable coupling to the second and third terminals ofeach of the cells, the method further comprising coupling the additionalcapacitor one of the cells; and from time to time, uncoupling theadditional capacitor from a cell and coupling the additional capacitorwith the controller comprising the driver, and driving the voltagethereof to a voltage level.
 5. A method for use with a battery controlapparatus for use with a battery composed of a multiplicity ofthree-terminal electrochemical cells, each cell having first and secondterminals, connected with respective electrodes, one of which is apositive terminal and one of which is a negative terminal, and each cellhaving a third terminal connected with a grid electrode, the batterycontrol apparatus comprising a multiplicity of modules eachcorresponding to one of the three-terminal electrochemical cells, eachmodule connected with the second and third terminals thereof, the methodcomprising: from time to time, controlling each of the modules so as todrive the voltage across the second and third terminals to a respectivevoltage level wherein each of the modules comprises a respective firstcapacitor and switchable coupling to the second and third terminals ofthe respective cell, the method further comprising coupling the firstcapacitor to its respective cell; from time to time, uncoupling one ofthe first capacitors from its respective cell and coupling the capacitorwith a controller comprising a driver, and driving the voltage thereofto a voltage level; and further comprising uncoupling the capacitor thatis coupled from the controller therefrom, and coupling the capacitor toits respective cell.